1. Technical Field
The invention relates to an optical record carrier recording method for forming marks and lands by applying a radiation beam to a recording surface of an optical record carrier, the radiation beam for each mark to be recorded being set to at least one write power level capable of forming a mark during a write power irradiation period and being set for each land section between the marks, to at least one bottom power level incapable of forming a mark during a bottom power irradiation period.
The invention also relates to an optical record carrier recording method for forming marks and lands by applying a radiation beam to a recording surface of an optical record carrier, the marks having a time length of nT, where T represents the time length of one period of a reference clock in a data signal and n represents a predetermined natural number.
The invention also relates to optical recording devices for carrying out such methods.
2. Related Art
A recording method of the kind set forth in the preamble is know from the Compact Disc Recordable (CD-R) System Description (also know as the Orange-book). A mark is formed by applying a radiation beam having a write power level, Pw, to a recording surface of an optical record carrier during a write power irradiation period. The time length of the write power irradiation period depends on the length of the mark to be recorded. The length of a mark is represented by a parameter nT, where T represents the time length of one period of a reference clock in a data signal and n represents a predetermined natural number. For a CD-R system n is in an range from 3 to 11.
The nominal constant linear velocity speed (CLV-speed) of the CD system is between 1.2 and 1.4 m/sec. In a CD-R system this nominal constant linear velocity speed will result in an average EFM (Eight to Fourteen Modulation) clock frequency of 4.3218 MHz. However the system is also specified to run at higher speeds such as for example four times the nominal speed (4xc3x97). Running at higher speeds, the write power level is enhanced with an extra power, xcex94P, at the beginning of the write power irradiation period. By applying this extra power, the degradation of the jitter due to of the high speed is somewhat reduced. The jitter is the standard deviation of the time difference between level transitions in a digitized read signal and the corresponding transitions in a clock signal, the time difference being normalized by the duration of one period of said clock.
It is a drawback of the known method that it does not allow a sufficient reduction of the jitter in the read signal obtained from reading marks recorded by using the know method, especially when the marks are recorded at high speeds such as, for example, eight times the nominal speed (8xc3x97).
It is an object of the invention to provide a method of recording marks of the kind described in the opening paragraph which offers reduced jitter.
This object is achieved by a method as described in the preamble which is characterized in that the radiation beam is set to at least one intermediate power level after the bottom power irradiation period and before the write power irradiation period, the intermediate power level being higher than the bottom power level and being set in accordance with a time length of the preceding bottom power irradiation period.
Marks are recorded on a recording surface by applying a radiation beam having a sufficiently high write power level to a location on the recording surface of an optical record carrier, thus temporarily increasing the local temperature of the recording surface. However, when recording a mark, the temperature of the actual location on the recording surface is pre-heated because of the recording of a previous mark. This so-called pre-heat effect results in an increase of particularly the leading edge jitter of the mark to be recorded. Furthermore, the recording of a mark slows down the cooling-down of the location of the previously recorded mark. This so-called post-heat effect results in an increase of particularly the trailing edge jitter of the previously recorded mark.
The influence of these thermal interference effects (that is, the pre-heat and the post-heat effect) depends on the distance between the actual location on the recording surface where a mark is to be recorded and the location of the previously recorded mark. Therefore, the influence of the thermal interference effects depends on the length of the land, lL, between the marks. This length can be expressed in the time length of the bottom power irradiation period, tL, because of the relation: tL=lL/actual CLV-speed.
The thermal interference effects can be reduced by introducing an intermediate power level after the bottom power irradiation period and before the write power irradiation period, the intermediate power level being dependent on the time length, tL, of the preceding bottom power irradiation period.
Version of the method according to the invention is characterized in that an intermediate power level following a first bottom power irradiation period having a time length of (n+1)T is set to be larger than or equal to an intermediate power level following a second bottom power irradiation period having a time length of nT.
The thermal interference effects between two marks decrease when the distance between the marks increases. Therefore the compensation for these effects obtained by introducing the intermediate power level needs to be less for larger distances than for shorter distance. Therefore, the intermediate power level will be closer to the write power level in the case of long distances between the marks.
A preferred version of the method according to the invention is characterized in that an intermediate power level following a first bottom power irradiation period having a time length of 3T is set within a range of from 0.50 to 0.80 times the write power level, that an intermediate power level following a second bottom power irradiation period having a time length of 4T is set within a range of from 0.75 to 0.95 times the write power level, and that an intermediate power level following a third bottom power irradiation period having a time length of mT, where m represents a predetermined natural number larger than 4, is set so as to be substantially equal to the write power level.
From experiments it was concluded that, when recording at a speed of eight (8xc3x97) to sixteen (16xc3x97) times the nominal speed, reduction of the jitter is obtained when the intermediate power level is within the above mentioned ranges. A particularly reduction of the jitter is obtained when an intermediate power level following a first bottom power irradiation period having a time length of 3T is set so as to be substantially equal to 0.65 times the write power level (11) and when an intermediate power level following a second bottom power irradiation period having a time length of 4T is set so as to be substantially equal to 0.85 times the write power level. However, the optimal setting of the intermediate power levels depend on properties of the optical record carrier used. Therefore, it is suggested that an Optimal Power Calibration (OPC) method should be used to determine the optimal settings of the intermediate power levels for each individual optical record carrier.
Version of the method according to the invention is characterized in that the time length of the intermediate power irradiation period is substantially equal to xc2xcT.
Although the time length of the intermediate power irradiation period may be set to any value, such as for example xe2x85x9T, xc2xdT and 1T, results are obtained for all recording speed when the intermediate power irradiation period is set so as to be substantially equal to xc2xcT.
At the nominal CLV-speed T represents a time length of 231.4 ns (=xc2xc0.3218 MHz). At a higher speed of eight times the nominal speed (8xc3x97) T represents a time length of 28.9 ns. An intermediate power level maintained for a time length of 7.2 ns (=T/4 at eight times nominal speed) can be easily and accurately obtained by means of contemporary electronics. Alternative methods for reducing the jitter employ a time shift of the leading-edge of the write power level. These time shifts typically occur in steps of T/20. At nominal speed these time shifts of 11.6 ns can also be obtained using contemporary electronics. However, at eight times the nominal speed (8xc3x97) these time shifts would be in the range of 1.4 ns, being a value being difficult to obtain accurately. At an even higher recording speed of sixteen times the nominal speed (16xc3x97), the time shifts would be in the range of 0.7 ns while the intermediate power level should be maintained for a time length of 3.6 ns
The object is also achieved by means of a method according to the invention which has the features as described in claim 7.
A further reduction of the jitter is obtained by applying a raised write power level when recording the marks, the raised power level being set in accordance with the time length of the mark to be recorded. For the shorter marks the raised power level is applied over the entire write power irradiation period. For the somewhat longer marks the raised power level is only applied to a portion at the end of the write power irradiation period. The time length of this portion may be equal for all marks or, alternatively, can be made dependent on the length of the mark to be recorded. For the longer marks no raised power level is applied.
A preferred version of the method according to the invention has the features as described in claim 8.
From experiments it was concluded that reduction of the jitter is obtained when the raised write power levels are within the specified ranges. A particularly reduction of the jitter is obtained when the first raised write power level, when recording a mark having a time length of 3T, is set so as to be substantially equal to 1.10 times the write power level and when the second raised write power level when recording a mark having a time length of 4T, is set so as to be substantially equal to 1.04 times the write power level.
Although the range specified for the first raised write power level overlaps with the range specified for the second raised write power level, the first raised power level is in general set to a higher value in comparison with the second raised write power level.
It is a further object of the invention to provide an optical recording device for carrying out the methods according to the invention.
This object is achieved by an optical recording device which has the features as described in claim 9. This object is also achieved by providing an optical recording device which has the features as described in claim 11.
Although the invention is explained by using a CD-R system as an example, it will be apparent to those skilled in the art that the invention may also be applied to alternative optical recording systems.